U.S. patent number 5,546,796 [Application Number 08/498,311] was granted by the patent office on 1996-08-20 for method and apparatus for measuring axle load of a running vehicle.
This patent grant is currently assigned to Omron Corporation. Invention is credited to Kunio Taniguchi.
United States Patent |
5,546,796 |
Taniguchi |
August 20, 1996 |
Method and apparatus for measuring axle load of a running
vehicle
Abstract
Axle load meters are arranged in an axle load measuring area of
a road. Instantaneous axle load values W.sub.1, W.sub.2, . . .,
W.sub.n are sampled from outputs of the axle load meters at time
points t.sub.1, t.sub.2, . . ., t.sub.n as measured from a time
point when the running vehicle enters the axle load measuring area.
Pairs of instantaneous axle load values (W.sub.1, W.sub.1+Tk),
(W.sub.2, W.sub.2+Tk), . . ., (W.sub.i, W.sub.i+Tk) at time points
(t.sub.1, t.sub.1+k), (t.sub.2, t.sub.2+k), . . ., (t.sub.i,
t.sub.i+k) each having a fixed time interval T.sub.k (k=1 to j) are
determined based on the measured instantaneous axle load values
W.sub.1, W.sub.2, . . ., W.sub.n, and average values W.sub.1Tk,
W.sub.2Tk, . . ., W.sub.iTk of the respective pairs are calculated,
to thereby produce average value groups for the respective fixed
time intervals T.sub.1, T.sub.2, . . ., T.sub.j. An average value
group having a minimum variation is selected from the average value
groups, and an average of the selected average value group is
employed as the axle load of the running vehicle.
Inventors: |
Taniguchi; Kunio (Kanagawa,
JP) |
Assignee: |
Omron Corporation
(JP)
|
Family
ID: |
15596374 |
Appl.
No.: |
08/498,311 |
Filed: |
July 5, 1995 |
Foreign Application Priority Data
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Jul 6, 1994 [JP] |
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6-154993 |
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Current U.S.
Class: |
73/146 |
Current CPC
Class: |
G01G
19/024 (20130101); G01G 19/035 (20130101) |
Current International
Class: |
G01G
19/03 (20060101); G01G 19/02 (20060101); E01C
023/00 () |
Field of
Search: |
;73/146,7,8 ;177/134
;364/426.02 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
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491655 |
|
Jun 1992 |
|
FR |
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WO92/21009 |
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Nov 1992 |
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WO |
|
Primary Examiner: Chilcot; Richard
Assistant Examiner: Oen; William L.
Attorney, Agent or Firm: Dickstein, Shapiro & Morin
Claims
What is claimed is:
1. An apparatus for measuring an axle load of a running vehicle,
comprising:
axle load meters arranged in an axle load measuring area of a
road;
means for measuring, using the axle load meters, instantaneous axle
load values W.sub.1, W.sub.2, . . ., W.sub.n at time points
t.sub.1, t.sub.2, . . ., t.sub.n, respectively, as measured from a
time point when the running vehicle enters the axle load measuring
area;
means for setting fixed time intervals T.sub.1, T.sub.2, . . .,
T.sub.j, where j is an integer not less than 2;
means for determining pairs of instantaneous axle load values
(W.sub.1, W.sub.1+Tk), (W.sub.2, W.sub.2+Tk), . . ., (W.sub.i,
W.sub.i+Tk) at time points (t.sub.1, t.sub.1+k), (t.sub.2,
t.sub.2+k), . . ., (t.sub.i, t.sub.i+k) each having a fixed time
interval T.sub.k, where k=1 to j, based on the measured
instantaneous axle load values W.sub.1, W.sub.2, . . ., W.sub.n,
and calculating average values W.sub.1Tk, W.sub.2Tk, . . .,
W.sub.iTk of the respective pairs, to thereby produce average value
groups for the respective fixed time intervals T.sub.1, T.sub.2, .
. ., T.sub.j ;
means for selecting an average value group having a minimum
variation from the average value groups; and
means for employing an average of the selected average value group
as the axle load of the running vehicle.
2. The apparatus of claim 1, wherein each interval between adjacent
ones of the time points t.sub.1, t.sub.2, . . ., t.sub.n has a
constant value .alpha., and the fixed time intervals T.sub.1,
T.sub.2, . . ., T.sub.j are integer multiples of the constant value
.alpha..
3. A method for measuring an axle load of a running vehicle based
on measurement outputs of axle load meters arranged in an axle load
measuring area of a road, comprising the steps of;
measuring, using the axle load meters, instantaneous axle load
values W.sub.1, W.sub.2, . . ., W.sub.n at time points t.sub.1,
t.sub.2, . . ., t.sub.n, respectively, as measured from a time
point when the running vehicle enters the axle load measuring
area;
setting fixed time intervals T.sub.1, T.sub.2, . . ., T.sub.j,
where j is an integer not less than 2;
determining pairs of instantaneous axle load values (W.sub.1,
W.sub.1+Tk), (W.sub.2, W.sub.2+Tk), . . ., (W.sub.i, W.sub.i+Tk) at
time points (t.sub.1, t.sub.1+Tk), (t.sub.2, t.sub.2+k), . . .,
(t.sub.i, t.sub.i+k) each having a fixed time interval T.sub.k,
where k=1 to j, based on the measured instantaneous axle load
values W.sub.1, W.sub.2, . . ., W.sub.n, and calculating average
values W.sub.1Tk, W.sub.2Tk, . . ., W.sub.iTk of the respective
pairs, to thereby produce average value groups for the respective
fixed time intervals T.sub.1, T.sub.2, . . . , T.sub.j ;
selecting an average value group having a minimum variation from
the average value groups; and
employing an average of the selected average value group as the
axle load of the running vehicle.
4. The method of claim 3, wherein each interval between adjacent
ones of the time points t.sub.1, t.sub.2, . . ., t.sub.n has a
constant value .alpha., and the fixed time intervals T.sub.1,
T.sub.2, . . ., T.sub.j are integer multiples of the constant value
.alpha..
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for
measuring the axle load of a running vehicle and, particularly, to
such a method and apparatus capable of performing computation in a
sufficiently short period by virtue of a small amount of
computation needed.
An apparatus is known which determines the weight of a running
vehicle by measuring vertical forces (hereinafter referred to as
axle loads) that are imparted to the road surface by the respective
axles of the vehicle and summing up the measured axle loads.
By the way, while running, a vehicle vibrates at resonance
frequencies corresponding to the entire body and respective
portions due to impacts that are caused by asperity of a road,
acceleration, etc. Therefore, the instantaneous vertical force
imparted to the road surface by an axle of a running vehicle varies
as shown in FIG. 7. In FIG. 7, the thin line indicates a waveform
corresponding to a main vibration of a running vehicle and the
thick line indicates a waveform corresponding to a combined
vibration of the main vibration and an auxiliary vibration of the
running vehicle. The main vibration means a resonance of the entire
vehicle and the auxiliary vibration means a resonance that occurs
at a portion of the vehicle or a load.
Thus, a waveform as shown in FIG. 7 is obtained when axle load
meters are arranged along a road and outputs of those axle load
meters are picked up upon passage of a vehicle. Conventionally, the
axle load of a running vehicle is determined from such a waveform
according to the following methods.
1) Wave components of an output of an axle load meter is dealt with
as errors. More specifically, the axle load of a running vehicle is
measured by an axle load meter installed at a selected measuring
location where vibration of a running vehicle is as small as
possible. The midpoint of vibration is directly determined from
outputs of the axle load meter, and employed as an axle load
measurement value of the running vehicle.
2) Axle load meters are stalled at a plurality of measuring
locations. A main vibration waveform corresponding to a resonance
frequency of the entire vehicle and an auxiliary vibration waveform
produced by a resonance at a portion of the vehicle are estimated
from a partial waveform obtained by those axle load meters. The
midpoint of vibration is determined from the estimated main
vibration waveform and auxiliary vibration waveform, and employed
as an axle load measurement value of the running vehicle.
3) To simplify method 2), a main vibration and an auxiliary
vibration are estimated with an assumption that the frequency of
the main vibration is equal to or around 3 Hz. The midpoint of a
resulting vibration is determined and employed as an axle load
measurement value of the running vehicle.
However, in method 1), in which a wave portion of an output of the
axle load meter is dealt with as errors, the measurement accuracy
is low even if the measurement by the axle load meter is performed
at a location where vibration of a running vehicle is as small as
possible. Further, method 1) has a problem that the axle load meter
installation point is restricted.
In method 2), in which a main vibration waveform corresponding to a
resonance frequency of the entire vehicle and an auxiliary
vibration waveform produced by a resonance at a portion of the
vehicle are estimated from a partial waveform obtained by the axle
load meters, the amount of computation becomes enormous and it is
therefore difficult to complete the computation in a required time
even with the use of a high-speed computer. Where vehicles pass
successively, the "required time" means a time from a time point
when the first vehicle passes a measuring point to a time point
when the second vehicle passes it.
Further, in method 2), the axle load meters are required to have
high measurement accuracy. In method 2), a vibration waveform of a
vehicle is computed, estimated and reproduced based on a partial
waveform measured by the axle load meters. Therefore, if the
accuracy of the axle load meters is low, measurement errors of the
axle load meters are amplified to prevent a correct
measurement.
In method 3), the frequency of a main vibration is assumed to be
equal to or around 3 Hz. Therefore, although method 3) is suitable
for measurements on large-sized vehicles having a main vibration
whose frequency is equal to or around 3 Hz, it may cause a large
error for other types of vehicles having a main vibration whose
frequency is not in that range. In addition, the reliability of
measurement data is low because not all large-sized vehicles have a
main vibration whose frequency is equal to or around 3 Hz.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and
apparatus for measuring the axle load of a running vehicle which
can not only produce measurement data that are within a stable
error range without amplifying measurement errors of each axle load
meter, but also produce highly reliable measurement data without
using a high-speed computer.
According to the invention, there is provided an apparatus for
measuring an axle load of a running vehicle, comprising:
axle load meters arranged in an axle load measuring area of a
road;
means for measuring, using the axle load meters, instantaneous axle
load values W.sub.1, W.sub.2, . . ., W.sub.n at time points
t.sub.1, t.sub.2, . . ., t.sub.n, respectively, as measured from a
time point when the running vehicle enters the axle load measuring
area;
means for setting fixed time intervals T.sub.1, T.sub.2, . . .,
T.sub.j, where j is an integer not less than 2;
means for determining pairs of instantaneous axle load values
(W.sub.1, W.sub.1+Tk), (W.sub.2, W.sub.2+Tk), . . ., (W.sub.i,
W.sub.i+Tk) at time points (t.sub.1, t.sub.1+k), (t.sub.2,
t.sub.2+k), . . ., (t.sub.i, t.sub.i+k) each having a fixed time
interval T.sub.k, where k=1 to j, based on the measured
instantaneous axle load values W.sub.1, W.sub.2, . . ., W.sub.n,
and calculating average values W.sub.1Tk, W.sub.2Tk, . . .,
W.sub.iTk of the respective pairs, to thereby produce average value
groups for the respective fixed time intervals T.sub.1, T.sub.2, .
. ., T.sub.j ;
means for selecting an average value group having a minimum
variation from the average value groups; and
means for employing an average of the selected average value group
as the axle load of the running vehicle.
In the above apparatus, each interval between adjacent ones of the
time points t.sub.1, t.sub.2, . . ., t.sub.n may have a constant
value .alpha., and the fixed time intervals T.sub.1, T.sub.2, . .
., T.sub.j may be integer multiples of the constant value
.alpha..
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a general configuration of an apparatus for measuring
the axle load of a running vehicle according to an embodiment of
the present invention;
FIG. 2 illustrates the principle of measuring an axle load value in
the invention; FIG. 3 is a functional block diagram showing a
configuration of a computer 30 shown in FIG. 1; FIG. 4 is a
flowchart showing an example of processing of a CPU shown in FIG.
3; FIG. 5 illustrates a method of calculating an instantaneous axle
load value W.sub.1+T with a fixed time interval of m.alpha.+.beta.;
FIG. 6 illustrates data tables stored in a memory of the CPU shown
in FIG. 3; and FIG. 7 is a graph showing the instantaneous vertical
force imparted to a road surface by the axle of a running vehicle
as a function of time.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A method and apparatus for measuring the axle load of a running
vehicle according to an embodiment of the present invention will be
described in detail with reference to the accompanying
drawings.
FIG. 1 shows a general configuration of an apparatus for measuring
the axle load of a running vehicle according to the embodiment of
the invention. In this embodiment, n axle load meters 20-1, 20-2,
20-3, . . ., 20-n are installed along a road 10 on which vehicles
(not shown) run. Measurement values of the respective axle load
meters 20-1, 20-2, 20-3, . . ., 20-n are sent to a computer 30 that
is connected to those axle load meters.
In this embodiment, each of the axle load meters 20-1, 20-2, 20-3,
. . ., 20-n has an effective measurement width (i.e., length along
the vehicle running direction on the road surface on which the axle
load meters are installed) of about 50 cm, and the interval between
the adjacent axle load meters is set at 40 cm. While these values
are selected in consideration of the fact that the interval between
the axles of one vehicle much varies with the kind of vehicle, it
is apparent that other various values may be used.
The measurement accuracy is improved as the number n of installed
axle load meters is increased. Where the width of each axle load
meter and the interval between the adjacent axle load meters are
respectively set at 50 cm and 40 cm and n is set at 7, highly
accurate measurements can be performed for vehicles running at 80
km/hour or less.
First, a description will be made of the principle of measuring an
axle load value in this embodiment.
In general, a main vibration of a vehicle running along the load 10
is represented by simple harmonic motion as shown in FIG. 2, which
satisfies
where .theta. denotes the phase.
In the simple harmonic motion of FIG. 2, if the midpoint of
arbitrary two points A1 and B1 of a measurable portion is denoted
by C1 and the midpoint of another two points A2 and B2 that are
close to the respective points A1 and B1 and have the same time
interval as the points A1 and B1 is denoted by C2, an average of C1
and C2 is located within the amplitude variation range of the
simple harmonic motion.
Further, plural pairs of points each of which are close to the
points A1 and B1 and have the same time interval as the points A1
and B1 are taken, and their plural midpoints are denoted by C2, C3,
. . . If a locus of the midpoints C1, C2, C3, . . . is flat, the
time interval between the points A1 and B1 is equal to (2n+1).pi.
from Equation (1) and the midpoints C1=C2=C3=. . . are located at
the center of the simple harmonic motion.
In this embodiment, pairs of instantaneous axle load values
(W.sub.1, W.sub.1+k), (W.sub.2, W.sub.2+k), . . ., (W.sub.i,
W.sub.i+k) respectively measured at (t.sub.1, t.sub.1 +k),
(t.sub.2, t.sub.2+k), . . ., (t.sub.i, t.sub.i+k) having a fixed
time interval T.sub.k are extracted from outputs of the n axle load
meters 20-1, 20-2, 20-3, . . ., 20-n. Further, average values
W.sub.1k, W.sub.2k, . . ., W.sub.ik of the respective pairs
(W.sub.1, W.sub.1+k), (W.sub.2, W.sub.2+k), . . ., (W.sub.i,
W.sub.i+k) are calculated.
An average W.sub.0k of the average values W.sub.1k, W.sub.2k, . .
., W.sub.ik is smaller than the maximum value and larger than the
minimum value of the main vibration of a running vehicle.
Therefore, by calculating the average W.sub.0k of the average
values W.sub.1k, W.sub.2k, . . ., W.sub.ik, i.e., by performing the
following calculation:
an axle load value of the running vehicle can be obtained from the
calculated value W.sub.0k.
According to the above method, the axle load value can be
determined with higher accuracy than method 1) where a wave portion
of an output of an axle load meter is dealt with as errors, and by
simpler calculations than methods 2) and 3).
To further improve the measurement accuracy of the axle load value,
a plurality of time intervals T.sub.1, T.sub.2, . . ., T.sub.j may
be set instead of employing the single fixed time interval T.sub.k
as in the above case. For each of the time intervals T.sub.k (k=1
to j), pairs of instant axle load values (W.sub.1, W.sub.1+k),
(W.sub.2, W.sub.2+k), . . ., (W.sub.i, W.sub.i+k) respectively
measured at (t.sub.1, t.sub.1+k), (t.sub.2, t.sub.2+k), . . .,
(t.sub.i, t.sub.i+k) having a time interval T.sub.k are extracted,
and average values W.sub.1k, W.sub.2k, . . ., W.sub.ik of the
respective pairs (W.sub.1, W.sub.1+k), (W.sub.2, W.sub.2+k), . . .
, (W.sub.i, W.sub.i+k) are calculated. Further, among plural groups
of average values W.sub.1k, W.sub.2k, . . ., W.sub.ik, a group
W.sub.1p, W.sub.2p, . . ., W.sub.ip having a minimum variation is
selected, and an average W.sub.0p of the average value group
W.sub.1p, W.sub.2p, . . ., W.sub.ip, which corresponds to a time
interval T.sub.p, is calculated such that
The value W.sub.0p is employed as the axle load value of the
running vehicle.
As is apparent from Equation (1), the time interval T.sub.p is
closest to 1/2 of the period of the main vibration of the running
vehicle. When the time interval T.sub.p is equal to 1/2 of the
period of the main vibration of the running vehicle, the average
value group W.sub.1p, W.sub.2p,. . ., W.sub.ip corresponds to the
auxiliary vibration of the running vehicle.
The average of a plurality of measurement values of the auxiliary
vibration having the center of the main vibration of the running
vehicle as the midpoint, i.e., the average of the values W.sub.1p,
W.sub.2p, . . ., W.sub.ip is approximated to the midpoint of the
auxiliary vibration as the number of sampling points is
increased.
Therefore, the axle load value can be obtained with high accuracy
by determining the average W.sub.0p of the average value group
W.sub.1p, W.sub.2p, . . ., W.sub.ip corresponding to the time
interval T.sub.p. The calculations for determining the axle load
value of the running vehicle is much simpler than in methods 2) and
3).
FIG. 3 is a functional block diagram showing a configuration of the
computer 30 shown in FIG. 1.
Referring to FIG. 3, the computer 30 consists of the following
components. Analog/digital converters 31-1, 31-2, 31-3, . . ., 31-n
correspond to the axle load meters 20-1, 20-2, 20-3, . . ., 20-n,
respectively. A clock generator 33 generates prescribed sampling
pulses. An input interface 32 takes in outputs of the
analog/digital converters 31-1, 31-2, 31-3, . . ., 31-n based on
the prescribed sampling pulses that are supplied from the clock
generator 33. A CPU 34 supervises the entire operation of the
computer 30. A memory 35 stores various data necessary for the
operation of the CPU 34.
Analog signals that are output from the axle load meters 20-1,
20-2, 20-3, . . ., 20-4 are converted to digital signals by the
analog/digital converters 31-1, 31-2, 31-3, . . ., 31-n, and taken
in by the CPU 34 via the input interface 32 based on the prescribed
sampling pulses supplied from the clock generator 33.
Measurement data that have been input to the CPU 34, i.e.,
measurement values (hereinafter called "instantaneous axle load
values") W.sub.1, W.sub.2, . . ., W.sub.n at time points t.sub.1,
t.sub.2, . . ., t.sub.n as measured from the entrance time of a
running vehicle into the axle load measuring area are temporarily
stored in the memory 35. If these values are plotted on a graph
(vertical axis: axle load; horizontal axis: time) in the same
manner as in FIG. 2, a waveform is obtained which is close to a
sine wave. Therefore, the axle load value can be determined
according to the measurement principle described above.
FIG. 4 is a flowchart showing an example of processing of the CPU
34 shown in FIG. 3.
First, j fixed time intervals T.sub.1 to T.sub.j are set in step 1.
The fixed time interval is an estimated value of the 1/2 period
which value is reversely calculated from a certain frequency.
Although the fixed time intervals T.sub.1 to T.sub.j may be set in
a variety of manners, in this embodiment they are set in the
following manner in consideration of the characteristics of the
main vibration of a running vehicle.
It is known that the frequency of the main vibration of a running
vehicle is 2-3 Hz when it is a large-sized vehicle, and is 3-5 Hz
when it is a small-sized vehicle. The 1/2-period range
corresponding to the frequency range of 2 to 5 Hz is 0.1 to 0.25
second. Therefore, it is effective to set T.sub.1 to T.sub.j within
the range of 0.1 to 0.25 second.
Further, if the fixed time intervals T.sub.1 to T.sub.j are set at
integer multiples of the pulse cycle (denoted by .alpha.) of the
clock generator 33, the following calculations are conveniently
performed which use the instantaneous axle load values W.sub.1,
W.sub.2, . . . , W.sub.n. It is however noted that setting the
fixed time intervals at integer multiples of .alpha. is not a
requisite.
A parameter k is set at 1 in step 2, and T.sub.k is substituted
into T in step 3. At this time, T is equal to T.sub.1, and the
following calculation is performed with the time interval
T.sub.1.
In step 4, all the pairs of instantaneous axle load values W.sub.1,
W.sub.2, . . ., W.sub.n which pairs have the time interval T are
extracted, and an average value of each pair of instantaneous axle
load values is calculated.
Where the fixed time interval is not an integer multiple m.alpha.
(m: integer) of the pulse cycle .alpha. but is, for instance,
m.alpha.+.beta.(0<.beta.<.alpha.), the measurement values
themselves of the instantaneous load cannot be used for the above
averaging. In this case, necessary values should be estimated.
Now, a description will be made of a method of estimating an
instantaneous axle load value W.sub.1+T at a time point
m.alpha.+.beta. after the time point t.sub.1 in calculating an
average value of an instantaneous axle load value W.sub.1 at
t.sub.1 and the instantaneous axle load value W.sub.1+T.
Referring to FIG. 5, since the pulse cycle is .alpha., if t.sub.n
and t.sub.n-1 are defined as
the time point m.alpha.+.beta. after the time point t.sub.1
satisfies
where m.alpha.+.beta.is the fixed time interval.
In this embodiment, as shown in FIG. 5, two points having
coordinates (t.sub.m+1, W.sub.m+1) and (t.sub.m+2, W.sub.m+2) are
connected to each other by a straight line, and the axle load
coordinate of a point located on that straight line and having a
time coordinate t.sub.1 +(m.alpha.+.beta.) is employed as
W.sub.1+T. Then, an average value of W.sub.1 and W.sub.1+.sub.T is
calculated. Since t.sub.m+2 -t.sub.m+1 =.alpha., W.sub.1+T is
calculated as
After all the average values have been calculated, a variation of
each average value group is calculated in step 5. Although there
are various methods of calculating the variation such as
calculating a difference between the maximum and minimum values of
an average value group, this embodiment employs the following
method. As shown in FIG. 6, an average W.sub.01 of respective
elements W.sub.1T1, W.sub.2T1, . . ., W.sub.iT1 (i: natural number)
of the average value group shown in data table-1 is calculated (see
data table-2). Then, absolute values (see data table-3) of
differences between W.sub.01 and the respective elements of the
average value group are averaged (see data table-4). By employing
an absolute value average W.sub.BT1 as a variation, even if there
exists an instantaneous axle load value that is far different from
the other values, its influence on the average can be made
small.
In step 6, it is judged whether the calculations have been
completed for all the j fixed time intervals. If the judgment
result is negative, k is incremented by 1 in step 7 and a variation
will be calculated in the similar manner for the next fixed time
interval. When the calculations have been completed for all the j
fixed time intervals, the minimum one (closest to 0) is determined
from the j variations thus calculated, and the average of the
average value group corresponding to the minimum variation is
employed as the axle load value (step 8).
With the above constitution, the invention provides the following
advantages:
1) Measurement values can be obtained within a stable error range
without amplifying measurement errors of the individual axle load
meters irrespective of the phase of a main vibration at an instant
when a running vehicle enters the axle load measuring area and its
relationship with the phase of an auxiliary vibration. Therefore,
the measurement values are highly reliable.
2) A wide variety of vehicles can be subjected to the measurement;
that is, the application of the invention is not limited to
vehicles whose main vibration has a frequency of 3 Hz.
3) Where the amplitude of an auxiliary vibration is smaller than a
main vibration, measurement values can be obtained with very high
accuracy.
4) By virtue of a small amount of computation, the computation can
be completed in a sufficiently short period even with a personal
computer. Therefore, all the vehicles passing successively can be
subjected to the measurement.
* * * * *